Devices and methods for bone fixation using axial implants

ABSTRACT

The invention comprises a method for fixating bones in the foot by aligning the bones in their desired position, inserting a screw in the aligned bones, inserting at least one transverse element near the head or tip of the screw, and tightening the screw to compress the bones. The screw comprises a shaft having first and second ends with spirally wound screw threads beginning near the first end and extending along the shaft. Advantageously, the screw is cannulated and screw threads are formed on an interior surface of the cannulation. Illustratively, the transverse elements may be staples, open-ended washers, or open-ended nuts. Reduction instruments and drill guides used in the invention are also disclosed.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.14/599,713, filed Jan. 19, 2015, which claims the benefit of divisionalof U.S. application Ser. No. 13/712,282, filed on Dec. 12, 2012, whichclaims the benefit of U.S. Provisional Application No. 61/569,464, filedDec. 12, 2011. The entire contents of these applications areincorporated herein by reference.

BACKGROUND

This invention relates to the field of orthopedic implant devices. Atypical application is as an intramedullary fixation assembly used forthe fixation of bones and the correction of deformities in the foot.

Orthopedic implant devices such as intramedullary nails, plates, rodsand screws are often used to repair or reconstruct bones and jointsaffected by deformity and disease such as Charcot arthopathy caused bydiabetes in some patients. Charcot arthopathy (or Charcot foot) is adestructive process affecting many regions including joints of the footand ankle in diabetics. Charcot arthopathy can affect any joint in thebody but is often seen in the foot. In the foot, the Charcot processtypically affects the tarsal and metatarsal bones and thetarsometatarsal and intertarsal joints which causes the foot to lose itsarch. This causes fragmentation, dislocation and fractures thateventually progress to deformity, instability and bony prominences. Footulcers may develop which often lead to deep infection and sometimesamputation.

FIG. 1 depicts a human foot 100 afflicted with Charcot arthopathy.Phalanges 110, the first metatarsal 120, medial cuneiform 130, navicular140, and talus 150 bones are depicted in foot 100. The deformity in thefoot will be apparent.

Early treatment for Charcot foot includes the use of therapeuticfootwear, immobilization of the foot, and/or non-weightbearingtreatment. Surgical treatments include orthopedic fixation devices thatfixate the bones in order to fuse them into a stable mass. Theseorthopedic implant devices realign bone segments and hold them togetherin compression until healing occurs, resulting in a stable mass.

Infection and complications are a major concern in these procedures.Wound closure is technically demanding for the surgeon, and devices thatadd surface prominence such as plates or exposed screws, add to thedifficulty by requiring greater tissue tension during incisionreapproximation. This increases the risk of post-operative woundinfections and dehiscence that may ultimately result in limb amputation.

There is therefore a need for improvements in intramedullary fixationassembly and methods of use that overcome some or all of the previouslydescribed drawbacks of prior art fixation assemblies and processes.

SUMMARY

The present invention is improved devices and methods for bone fixation.

The improved devices include a screw for use in fixating the bones andthe combination of the screw with at least one transverse element foruse in compressing the bones. In a preferred embodiment, the screwcomprises a shaft having first and second ends with spirally wound screwthreads beginning near the first end and extending along the shaft.Advantageously the screw is cannulated and screw threads are formed onan interior surface of the cannulation.

When the screw is implanted in a patient's foot, at least one transverseelement is secured to the screw near its first or second end. By way ofexample but not limitation, the transverse elements may be staples,open-ended washers, or open-ended nuts. The screw is then tightenedcausing the bones along the screw to be compressed.

Broadly, the methods of the invention comprise aligning the bones intheir desired position, inserting a screw in the aligned bones,inserting at least one transverse element near the head or tip of thescrew, and tightening the screw. Further details of the process are setforth below.

Instruments are also disclosed for use in practicing the invention.These include reduction instruments for use in aligning the bones and adrill guide for drilling holes adjacent the screw where one or moretransverse elements may be inserted.

Numerous variations may be practiced in the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention will beapparent to those of ordinary skill in the art in view of the followingdetailed description in which:

FIG. 1 depicts a human foot afflicted with Charcot arthopathy;

FIG. 2 is a cross-section of an illustrative embodiment of a screw ofthe present invention;

FIG. 3 is a flow chart depicting illustrative steps of an embodiment ofthe invention;

FIG. 4 depicts a reduction instrument used in the practice of theinvention;

FIGS. 5, 6, 8-11, and 15 depict details of certain of the steps of FIG.3;

FIG. 7 depicts a drill guide used in the practice of the invention; and

FIGS. 12-14 depict several transverse elements that may be used in thepractice of the invention.

DETAILED DESCRIPTION

FIG. 2 is a cross-section of an illustrative embodiment of a screw 200that may be used in the practice of the invention. Screw 200 has anelongated shaft 210 having first and second ends 220, 225 and alongitudinal axis A-A extending along the shaft. Preferably, the shaftis cannulated having a bore 230 that extends from first end 220 tosecond end 225. On an exterior portion of the shaft near the first end220 are spirally wound threads 240 that begin at approximately the firstend 220 of the shaft. There may be a head 250 on the shaft at its secondend 225. The diameter of the head may be wider than the diameter of theshaft. Alternatively, the head may be set off from the remainder of theshaft by a recess that circumscribes the shaft such as shown at 252 inFIG. 6. The invention may also be practiced using a screw in which thereare threads at the second end of the screw in place of a head.

The head of the shaft includes a recess 255 open to the end of the shaftthat is shaped to receive an instrument such as a screw driver or wrenchin driving engagement. For example, by way of illustration but notlimitation, the recess may be hexagonal in shape so as to receive ahexagonally shaped wrench similar to an Allen wrench or the like; or therecess may be slotted so as to receive the slotted blade of a screwdriver. Alternatively, there may be no recess in the head; and the headmay be shaped, for example, in a hexagon, to receive an instrument suchas a socket wrench or the like.

Optionally, numerous other refinements may be made in the constructionof the screw. For example, the screw may be reinforced at points whereforces are concentrated during use of the screw such as the point 242where exterior screw threads 240 end. The threads may also be tapered atpoint 242. Spirally wound threads may also be formed on an interiorsurface 232 of the bore 230. Such threads can facilitate extraction ofthe screw if that becomes desirable. The screw may also be treated byvarious processes to increase its strength.

FIG. 3 is a flow chart depicting illustrative steps of an embodiment ofthe invention used to treat Charcot arthopathy. It will be understoodthat the flow chart is only illustrative, that the order of execution ofsome steps may vary, and that some steps may not need to be used in thetreatment of a particular patient in accordance with the invention.Initially, an incision is made in the foot at step 310 to expose themetatarsal. Illustratively, the incision is a doral Lis Franc incision.Next, the foot is “gunstocked” at step 315. The bones of the foot,typically the metatarsal, cuneiform, navicular and talus are thenaligned at step 315 in the desired final position using a guide wire(e.g., a K-wire) to secure the bones in the desired alignment.

Illustratively, the guide wire is inserted into the bones using areduction instrument such as instrument 400 of FIG. 4. Instrument 400comprises a hollow sleeve 410 mounted on a handle 420. Sleeve 410 has acutting tip 430 on the end of the sleeve remote from the handle. A bore435 extends through sleeve 410 and handle 420 having an inside diameterthat is large enough to allow passage of a guide wire 440.

The diameter of guide wire 440 that may be used in the practice of theinvention can vary considerably depending on the patient and thesurgeon's preferences. Illustratively, the diameter is in the range ofapproximately 1.0 to 4.0 millimeters (mm). Different sleeve lengths maybe used in the practice of the invention depending on the size of thebones that are to be aligned. Advantageously, instrument 400 is usedwith guide wire 440 sticking through tip 430, which allows guide wire440 to be seated and unseated in the bone. Advantageously, the other endof guide wire 440 is keyed in handle 420 so that it can be easilymaneuvered by the handle.

After the bones are aligned on the guide wire as described above,instrument 400 is removed from the guide wire. Returning to the flowchart of FIG. 3, a drill bit is then mounted on the guide wire; and aborehole is drilled at step 325 through one or more of the alignedbones. This step is illustrated in FIG. 5 which depicts drill bit 510 onguide wire 440 boring a hole in the aligned bones, in this example, thefirst metatarsal, the medial cuneiform, the navicular, and the talusbones of a left foot. The drill is then removed; and a cannulated screwsuch as screw 200 of FIG. 2 is mounted on the guide wire at step 330.Screw 200 is then screwed into the borehole at step 335 using a screwdriver 600 as shown in FIG. 6.

A drill guide is then mounted on the screw at step 345. The drill guideis used at step 350 to guide a drill bit in forming first and secondholes on opposite sides of the screw at a first position that typicallyis just below the head of the screw. In forming these holes, the drillbit breaks the cortex of the bone on either side of the screw at thefirst position. The drill guide is also used at step 355 to guide anosteotome that cuts the cortex of the bone between the first and secondholes at the first position. Next, an element of the drill guide ispositioned at a second position above the threaded portion of the screwat step 360. This element is then used at step 365 to form at least onepair of third and fourth holes on opposite sides of the screw at thesecond position. Again, the drill bit breaks the cortex of the bone oneither side of the screw in the second position. This element is alsoused at step 370 to guide an osteotome that cuts the cortex of the bonebetween the third and fourth holes at the second position. The drillguide is then withdrawn at step 375.

The drill guide is shown as guide 700 in FIG. 7 and its use is depictedin FIGS. 8-11. Guide 700 comprises a screw mount 710 that is screwed orclamped onto screw 200 so that it is aligned with the longitudinal axisA-A of screw 200. The guide further comprises a bracket 720 that ismounted on the screw mount 710 and an extension arm 730 that is mountedon bracket 720 so that the arm extends parallel to the longitudinal axisof screw 200. Bracket 720 encloses first and second holes 722, 724 and aslot 726 that extends between the first and second holes. Extension arm730 encloses several sets of third and fourth holes 732, 734 and a slot736 that extends between the third and fourth holes. The first andsecond holes are located in bracket 720 at a position such that whenbracket 720 is securely mounted on screw 200, the holes are on oppositesides of the screw at the first position on the screw. Extension arm 730can be positioned so that the third and fourth holes are on oppositesides of the screw at the second position on the screw. The several setsof holes 732, 734 and slot 736 make it possible to locate severaltransverse elements at the second position. A ruler on the extension armallows the surgeon to locate the second position with precision.

FIG. 8 depicts screw mount 710 and bracket 720 mounted on screw 200.FIG. 9 depicts the use of hole 724 to guide a drill bit 922 in drillinga hole into the cortex adjacent screw 200 in the first position; andFIG. 10 depicts the use of slot 726 to guide an osteotome 1026 inbreaking a hole in the cortex around screw 200 at the first position.FIG. 11 depicts screw mount 710, bracket 720 and extension arm 730cooperating to locate the sets of third and fourth holes 732, 734 andslot 736 at a second position on the screw.

Returning to the flow chart of FIG. 3, at step 380, the two ends of astaple, an open washer, an open nut or the like are inserted into thefirst and second holes at the first position; and the two ends of one ormore staples, open washers, open nuts or the like are inserted into thethird and fourth holes at the second position. The staples, washers,nuts as the case may be are then driven at step 385 into their finalposition in the cortex so that they engage the screw at the firstposition near the head and engage the screw threads at the secondposition.

FIG. 12 depicts the profile of an open washer or open nut 1200. FIG. 13depicts the profile of an open washer or open nut 1300 in positionaround screw 200. FIG. 14 depicts a staple 1400 in position around screw200. In each case, each washer or nut 1200, 1300 and each staple 1400has two spaced-apart ends 1210, 1212; 1310, 1312; 1410, 1412 joined by amiddle portion 1214, 1314, 1414, respectively. The middle portion may bestraight as in the case of a conventional staple or rounded to varyingdegrees thereby approximating the curvature of the exterior of thescrew. For convenience, the various elements such as staples, openwashers, open nuts and the like that may be used in the practice of theinvention will be referred to as transverse elements.

A screw driver is then used at step 390 to turn the screw so as to bringcloser together the transverse elements at the first and secondposition, thereby compressing the bones between these positions. This isillustrated in FIG. 15 which depicts a screw driver 1500 being used toturn screw 200 to move staples 1510 and 1520 closer together. When thisstep is completed, the screw driver is then removed and the incision isclosed at step 395.

As will be apparent to those skilled in the art, numerous variations maybe practiced within the spirit and scope of the present invention. Forexample, a variety of different tools—screw drivers, wrenches, reductioninstruments and drill guides—may be used in the practice of theinvention. Screws of different sizes and different shapes may be used.Likewise different transverse elements may be used. There may also bevariation in the procedure used to implant the screw and transverseelements in the foot. For example, certain steps can be skipped orcombined with other steps and certain steps can be performed in adifferent order. In some procedures it may not be necessary to inserttransverse elements at both the first and second positions. For example,it may be possible to develop sufficient compression between the head ofthe screw and one or more transverse elements located on the screwthreads that a transverse element near the head of the screw is notneeded. Alternatively, it may be possible to develop sufficientcompression between the screw threads and a transverse element mountednear the screw head that one or more transverse elements mounted on thescrew threads are not needed. When transverse elements are used at boththe first and second positions, the holes can be drilled at the secondposition before they are drilled at the first position; or it may not benecessary to drill the holes at one or both positions because it may bepossible to insert the transverse elements at the appropriate positionsaround the screw using other devices. Similarly, it may not be necessaryto use the osteotome at one or both positions.

The invention claimed is:
 1. An assembly for bone fusion, comprising: ascrew member comprising an elongated body extending from a first end toa second end, wherein the elongated body includes first threads near thefirst end and second threads near the second end; a first transverseelement that engages the first threads of the elongated body of thescrew member such that the screw member can be rotated with respect tothe first transverse element; and a second transverse element thatengages the second threads of the elongated body of the screw membersuch that the screw member can be rotated with respect to the secondtransverse element; wherein the first transverse element comprises twospaced-apart ends joined by a middle portion.
 2. The assembly of claim1, wherein the first transverse element engages a first bone, whereinthe second transverse element engages a second bone, and whereinrotating the screw member brings the first and second transverseelements closer together thereby compressing the first and second bones.3. The assembly of claim 1, wherein the elongated body is cannulated. 4.The assembly of claim 3, wherein the cannulated elongated body has aninterior surface that is threaded.
 5. The assembly of claim 1, whereinthe elongated body comprises a recess at the first end that is shaped toreceive an instrument.
 6. The assembly of claim 1, wherein the first andsecond transverse elements comprise different shapes.
 7. An assembly forbone fusion, comprising: a screw member comprising an elongated bodyextending from a first end to a second end, wherein the elongated bodyincludes a first continuous thread along the exterior surface of theelongated body near the first end and a second continuous thread alongthe exterior surface of the elongated body near the second end, whereinthe screw member is inserted in a bore extending through at least afirst bone and a second bone; a first transverse element that engagesthe first continuous thread such that the screw member can be rotatedwith respect to the first transverse element, wherein the firsttransverse element engages the first bone; and a second transverseelement that engages the second continuous thread such that the screwmember can be rotated with respect to the second transverse element, andwherein rotating the screw member brings the first and second transverseelements closer together thereby compressing the first and second bones;wherein the first transverse element comprises two spaced-apart endsjoined by a middle portion.
 8. The assembly of claim 7, wherein theelongated body is cannulated.
 9. The assembly of claim 8, wherein thecannulated elongated body has an interior surface that is threaded. 10.The assembly of claim 7, wherein the elongated body comprises a recessat the first end that is shaped to receive an instrument.
 11. Theassembly of claim 7, wherein the first and second transverse elementscomprise different shapes.
 12. An assembly for bone fusion, comprising:a screw member comprising an elongated body extending from a first endto a second end, having threads at the first end and threads at to thesecond end; a first transverse element that engages the threads at thefirst end of the elongated body of the screw member such that the screwmember can be rotated with respect to the first transverse element; anda second transverse element that engages the threads at the second endof the elongated body of the screw member such that the screw member canbe rotated with respect to the second transverse element; whereinrotating the screw member brings the first and second transverseelements closer together; wherein the first transverse element comprisestwo spaced-apart ends joined by a middle portion.
 13. The assembly ofclaim 12, wherein the elongated body is cannulated.
 14. The assembly ofclaim 13, wherein the cannulated elongated body has an interior surfacethat is threaded.
 15. The assembly of claim 12, wherein the elongatedbody comprises a recess at the first end that is shaped to receive aninstrument.
 16. The assembly of claim 12, wherein the first and secondtransverse elements comprise different shapes.
 17. The assembly of claim13 wherein the first and second transverse elements comprise differentshapes.